easiest way to do it is
remove ls1
oil pressure sensor
break off plastic part and dig out electrics
u will have an alloy piece left
drill and tap the centre to suit your new
oil pressure sender
with water u can make or buy adaters to screw into drivers side head right at back
u just have to remome allen key bolt
i have run out of the adpaters but i can get more easily when i order some other stuff
from my guy who makes em
or u can drill and tap a hole in flat sevtion on water pump
if u fit a sensor in a pipe between radiator and engine make sure u weld a small nut so u can run n earth wire from pipe/sensor to ground or your sender will not be earthed and gauge wont work